Vibrato producing circuit for electronic musical instrument



20, 1960 s, -row r 2 ,953,054

VIBRATO PRODUCING CIRCUIT FOR ELECTRONIC MUSICAL INSTRUMENT Filed Aug. 14, 1955 3 heet 1 VIBR INVENT R5. QQ JP1%%PZ%EM Sept. 20, 1960 S. HEYTOW ETAL VIBRATO PRODUCING CIRCUIT FOR ELECTRONIC MUSICAL INSTRUMENT Filed Aug. 14, 1953 3 Sheets-Sheet 2 INVENTO fi gazcz If/$115012,

Sept. 20, 1960 s. HEYTOW EIAL 2,953,054

VIBRATO PRODUCING CIRCUIT FOR ELECTRONIC MUSICAL INSTRUMENT Filed Aug. 14, 1953 5 Sheets-Sheet 3 IHI M I 'F United States Patent VIBRATO PRODUCING CIRCUIT FOR ELEC- TRONIC MUSICAL INSTRUMENT Solomon Heytow, 8013 Merrill Ave., and Richard H. Peterson, 8918 S. Elizabeth St., both of Chicago, Ill.

Filed Aug. 14, 1953, Ser. No. 374,202

6 Claims. (Cl. 84--1.2'5)

Our invention relates to electronic musical instruments and includes among its objects and advantages improved means for developing a vibrato effect in an electronic musical instrument.

In the accompanying drawings:

Figure 1 is an assembled block diagram of a portion of a musical instrument according to the invention;

Figure .2 is a section of a selenium rectifier;

Figure 3 is a perspective, partly in section, of a voltagesensitive resistor;

Figure 4 is a wiring diagram of an oscillator provided with means for producing a vibrato;

Figure 5 is a wiring diagram of the same oscillator with a different vibrato means; and

Figure 6 is a wiring diagram of the same oscillator with a third vibrato means.

In the embodiment of the invention selected for illustration, and referring first to Figure 1, there are indicated three tone-generating units 10, 12, and 14. Each of these units may be a conventional Hartley oscillator, which is a type well known to those skilled in the art. Each oscillator delivers a wave of dependably constant frequency and substantially sine curve shape. A complete organ bank would call for sixty one, or seventy three, or eighty five such oscillators, one for the pitch corresponding to each note to be produced.

Each of the entire series of oscillators is selectively controlled by the player by its selective key switch 38, which receives activating potential from the bus 39.

The output from each of the oscillators 10, 12, and 14 is connected to each of six wave-shaping units 16, 18, 20, 22, 24, and 26.

For convenience in discussing thet functioning of the parts involved, rectifying means, considered in connection with the specific functions described in this inven tion, may conveniently be referred to as of two sorts, substantial and absolute. The well-known selenium rectifying plate has a very low resistance in one direction it still conducts current, with a resistance that may be from fifty to five thousand times as great as in the low-resistance direction. However, a diode or triode vacuum tube can be made to conduct current easily in one direction and not at all in the opposite direction. Such a rectifier is an absolute rectifier, and the characteristics with respect to which it differs from a substantial rectifier are advantageous in some combinations and disadvantageous in others.

Referring now to Figure 4, it will be obvious that the frequency characteristics of the circuit containing the inductor 92 and capacitor 94 may be varied by changing the constants of the circuit with respect to either the capacitance or the inductance, and most conveniently by changing the capacitance. In Figure 4 we have indicated a capacitor 114 connected to point 110, and through a voltage-sensitive resistor 118, to bus bar B The variable D.C. potential source 112 may be connected with bus bar B, by selective switch 122. With bus bar B unbiased,

Patented Sept. 20, 1960 the frequency of the oscillation may be tuned to the exact pitch desired. Subsequently, if the operator connects B to the variable potential source 112, by means of selective stop switch 122, bus bar B assumes a voltage which fluctuates at the desired low frequency. This renders the capacitor 114 effective whenever the potential of the bus bar rises to the point where resistor 118 becomes a low resistance. The ordinary resistance 132 is needed to carry the DC. current that controls the voltagesensitive resistor 118. This arrangement can produce an excellent vibrato.

-In Figure 5 we have illustrated a capacitor 124 corresponding to capacitor 114 and connected to bus bar B through a resistor 126. But the ground connection is through a voltage-sensitive resistor 128. This arrangement gives a very pleasing and smooth vibrato.

A diiferent arrangement is indicated in Figure 6. The potential of the bus B of course, oscillates with respect to ground, and the point is connected to bus B through a capacitor shunted by resistor 132, and with loop in series with a selenium rectifier 134 arranged in the direction to permit current to flow when the bus has a positive potential. This arrangement produces a smooth, pleasant vibrato. Furthermore, the selenium rectifier can be replaced with one of copper oxide or with a voltage-sensitive resistance of fairly high value.

One form of voltage-sensitive resistor with which good results have been secured, is illustrated in Figure 3. It comprises a disk 136 of granular silicon carbide mixed with ceramic binder and fired at high temperature, with metal conducting plates 138 afiixed to both sides. We have illustrated the plates 138 plated on the silicon carbide disk and soldered to wire connectors 140 and 142. The voltage-sensitive resistor is non-polar, i.e., its resistance characteristics are identical regardless of the direction of the applied voltage.

Referring now to Figure 2, one form of rectifier with which satisfactory results have been obtained is a simple tube 144 of insulating fiber threaded at both ends to receive a metal top plug 146 and bottom plug 148. For convenience in assembly, both plugs may be slotted to receive a screw driver. External leads 150 and 152 are convenient for connecting the device into a circuit. Inside the tube 144 we provide a thin metallic plate 154 having a small central boss or tit abutting the plug 148. The annular space around the boss is filled in with an in sulating washer 158.

The boss consists of a layer 155 of selenium, and a layer 146 of Woods metal. -A light compression coil spring bears at its upper end against the plug 146 and at its lower end against the plate 154. This keeps the boss 156 in effective contact with the plug 148 and establishes an electrical connection through the device. A convenient size for such a device is about a quarter of an inch in diameter and three-fourths of an inch long. In such small sizes it is convenient to form the plate 154 by stamping it out of a large plate, one side of which has previously been coated with selenium and then with Woods metal. Then the disk is placed in a small lathe and turned down to final shape. This leaves a contact area ample for the extremely small currents involved, and at the same time reduces the condensor action at the contact surface to a very minor fraction of what it would be if the contact surface were the entire area of the plate 154.

Such a device has a low conductivity when the terminal 150 is negative and relatively high conductivity when that terminal is positive. In the wiring diagrams the arrow points in the direction of low resistance conductivity.

Others may readily adapt the invention for various conditions of service by employing one or more of the novel features disclosed or equivalents thereof. As at present advised with respect to the apparent scope of our invention, we desire to claim the following subject matter.

This application is a continuation in part of our copending application Serial Number 195,222, filed November 13, 1950.

We claim: 7

1. An electronic musical instrument comprising, in combination: a series of independent audio frequency oscillators, one for each semitone of the musical scale throughout the range of the instrument; each oscillator having a tank circuit of constant frequency; each'tank circuit comprising inductance and capacitance connected in parallel; detuning means for each oscillator comprising a supplemental capacitance adapted to lower the normal tank circuit frequency; an electrical connection for rendering said ancillary detuning means operative; said electrical connection including a resistor of the silicon carbide type, sensitive to impress voltage at constant temperature; a separate D.-C. circuit for passing direct current through said voltage-sensitive resistor to change its resistance; automatic means for varying the direct current potential on said resistor smoothly from maximum to minimum with vibrato frequency; and player-operated switch means for rendering said automatic means continuously operative or continuously inoperative.

2. An instrument according to claim 1 in which said automatic means includes a continuously operative source of varying DC. potential, and said player-operative switch means is constructed and arranged to connect and disconnect said source and said DiC. circuit.

3. An instrument according to claim 1 in which said D.C. circuit includes a protective resistor in series with said voltage-sensitive resistor.

4. An instrument according to claim 3 in which said protective resistor is shunted across said supplemental capacitance.

5. An electronic musical instrument comprising, in combination: a series of audio-frequency oscillators for the semi-tones of the musical scale; each oscillator having a tank circuit of stable frequency; each tank circuit comprising inductance and capacitance connected to store and exchange energy at a predetermined frequency; frequency-changing means operatively associated with each oscillator comprising a series-connected diode sensitive to variations in impressed potential; a circuit connected to said diode for selectively impressing potential on said diode to control its impedance; automatic repetitive vibrato producing means operatively associated with said circuit for intermittently varying the impressed potential in said separate circuit to change the frequency of said oscillator in vibrato fashion; and player-operated means operatively associated with said automatic means for rendering said automatic means continuously operative or continuously inoperative; said automatic means operating at vibrato frequency.

6. An electrical musical instrument comprising, in combination: a series of audio-frequency oscillators, one for each semi-tone of the musical scale; each oscillator having a tank circuit of constant frequency; each tank circuit comprising an inductor and a main capacitor; detuning means operatively associated with each oscillator comprising a supplemental capacitor for lowering the normal tank frequency; an electrical connection for rendering said supplemental capacitor operative by connecting it in parallel with said main capacitor; said electrical connection including a diode sensitive to variations in impressed potential; 21 separate D.C. circuit operatively associated with said diode for impressing D.C. potential on said diode to change its resistance; automatic vibrato producing means operatively associated with said circuit for varying the impressed potential on said diode to change its resistance intermittently for producing a vibrato effect; and player-operated switch means operatively associated with said automatic means for rendering said automatic means continuously operative or continuously inoperative.

References Cited in the file of this patent UNITED STATES PATENTS 2,182,377 Guanella Dec. 5, 1939 2,190,078 Markowitz Feb. 13, 1940 2,323,392 Hammond et a1 July 6, 1943 2,328,282 Kock Aug. 31, 1943 2,418,842 Kinsburg Apr. 15, 1947 2,470,705 Larsen May 17, 1949 2,486,208 Rienstra Oct. 25, 1949 2,580,424 Hanert Jan. 1, 1952 2,677,799 Foster et al May 4, 1954 FOREIGN PATENTS 362,377 Great Britain Nov. 27, 1931 654,206 Germany Dec. 14, 1937 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,953 O54 September 20, 1960 Solomon Heytow et al.

It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l line 47 for "that" read the line 58, for "tion it still" read tion but in the other direction it still column 2 line 21, for "with loop" read with this loop line 49 for "146" read 156 Signed and sealed this 4th day of April 19610 (SEAL) Attest; ERNEST W. SWIDER TQX ARTHUR W. CROCKER UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,953 O54 September 20, 1960 Solomon Heytow et al.

It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l line 47 for "that" read the line 58, for "tion it still" read tion but in the other direction it still column 2 line 21, for "with loop" read with this loop line 49 for "146" read 156 Signed and sealed this 4th day of April 19610 (SEAL) Attest; ERNEST W. SWIDER TQX ARTHUR W. CROCKER UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2353 054 September 20, 1960 Solomon Heytow et a1.

It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1 line 47, for "thet" read the line 53, for "tion it still" read tion,, but in the other direction it still column 2 line 21 for "with loop" read with this loop line 4 .9 for "146" read 156 Signed and sealed this 4th day of April 1961,

(SEAL) Attest:

v "t ARTHUR w. CROCKER Attesting Oflicer Acting Commissioner of Patents 

